<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <!--内部JS
        外部JS-->
    <script>
        alert("Hello World");
    </script>
    <script src="js/a.js"></script>
</head>
<body>
    <input type="text">
</body>
</html>